1. Field
The present application pertains generally to communications, and more specifically, to discovery of neighbor cells in E-UTRAN.
2. Background
In the 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE), network nodes have a logical connection to each other over an IP transport. In the decentralized architecture, Node B may be considered to be attached to the network in a “plug-n-play” manner, wherein Node B self-configures operation parameters. It is expected that Node B will use information provided by user equipment (UE). Then the Node B may establish an association with the neighbor cells. However, in the prior art, the UEs do not know the IP addresses of those neighboring cells, the UEs just provide a cell ID.
Universal Mobile Telecommunications System (UMTS) is one of the third-generation (3G) mobile telephone technologies (or 3rd Generation Wireless Mobile Communication Technology). A UMTS network consist of 1) a core network (CN), 2) a UMTS terrestrial radio access network (UTRAN) and 3) user equipment (UE). The core network work provides routing, switching, and transit for user traffic. A Global System for Mobile Communications (GSM) network with General Packet Radio Service (GPRS) is the basic core network architecture that UMTS is based on. The UTRAN provides the air interface access method for User Equipment. A base station is referred as Node B and control equipment for Node Bs is called a radio network controller (RNC). For an air interface, UMTS most commonly uses a wideband spread-spectrum mobile air interface known as wideband code division multiple access (or W-CDMA). W-CDMA uses a direct sequence code division multiple access signaling method (or CDMA) to separate users.
A UMTS Terrestrial Radio Access Network (UTRAN) is a collective term for the Node Bs (or base stations) and the control equipment for the Node Bs (or radio network controllers (RNC)) it contains which make up the UMTS radio access network. This is a 3G communications network which can carry both real-time circuit switched and IP based packet switched traffic types. The RNC provides control functionalities for one or more Node Bs. Connectivity is provided between the UE (user equipment) and the core network by the UTRAN.
The UTRAN is connected internally or externally to other functional entities by four interfaces: Iu, Uu, Iub and Iur. The UTRAN is attached to a GSM core network via an external interface called Iu. A radio network controller (RNC) supports this interface. In addition, RNC manages a set of base stations called Node Bs through interfaces labeled Iub. The Iur interface connects two RNCs with each other. The UTRAN is largely autonomous from the core network since the RNCs are interconnected by the Iur interface. FIG. 1 discloses a communication system which uses the RNC, the Node Bs and the Iu and Uu interfaces. The Uu is also external, connects the Node B with the UE, while the Iub is an internal interface connecting the RNC with the Node B.
The RNC fills multiple roles. First, it may control the admission of new mobiles or services attempting to use the Node B. Second, from the Node B, i.e. base station, point of view, the RNC is a controlling RNC. Controlling admission ensures that mobiles are allocated radio resources (bandwidth and signal/noise ratio) up to what the network has available. It is where Node B's Iub interface terminates. From the UE, i.e. mobile, point of view, the RNC acts as a serving RNC in which it terminates the mobile's link layer communications. From the core network point of view, the serving RNC terminates the Iu for the UE. The serving RNC also controls the admission of new mobiles or services attempting to use the core network over its Iu interface.
Cell searching is the procedure by which a UE acquires time and frequency synchronization with a cell and detects the cell ID of that cell. Two signals (“channels”) transmitted in the downlink, the “SCH” (Synchronization Channel) and “BCH” (Broadcast Channel) may be used in a universal terrestrial radio access (or UTRA) cell search. In the UMTS system, UTRA identifies the time division duplex (TDD) and the frequency division duplex (FDD) access mode. The primary purpose of the SCH is to acquire the timing, i.e., at least the SCH symbol timing, and frequency of the received downlink signal. The BCH broadcasts a set of cell and/or system-specific information which may be similar to the current UTRA BCH transport channel. Aside from the SCH symbol timing and frequency information, the UE acquires cell-specific information such as the cell ID. To facilitate cell ID detection, the cell ID may be embedded into the SCH. For example, the cell ID may be directly mapped into the SCH, or different cell ID information may be group-wised. For the case of group ID, cell ID group index can be detected using the SCH, and the cell IDs within the detected cell ID group can be detected using reference symbols or the BCH. As an alternative approach, information regarding the BCH bandwidth and CP length may be detected by blind detection from the SCH or BCH, by using hypothesis testing for example. FIG. 2 is a flowchart disclosing the basic cell search procedure.